1. Field of the Invention
The present invention concerns a process for the alignment of an electro-optical solid state device on an optical fiber, in order to obtain an optical head, i.e. an electro-optical component, that is an assembly contained in a sealed closed housing and acting as interface between an electronical part and an optical part. The process according to the invention is dynamic, i.e. the solid state device and the fiber operate during their respective positioning. The invention concerns optical heads aligned according to said invention.
An electro-optical component, called optical head, comprises inside a protective housing:
in every case, a light emitting or receiving semiconductor chip, and a light line, PA1 in frequent case, feed-back and electronic elements such as feed or control elements or protection elements and possibly control electronics.
The semiconductive chip can be a laser diode, an electroluminescent DEL diode, a PIN diode, for example, for the reception. The light line comprises an optical fiber and often a focusing microoptic in the form for example of a lens at the end of the optical fiber. The feed-back elements included in the housing can be elements for controlling the emitted light, or the temperature, for example.
The electro-optical components suitable to be aligned according to the process described in the present invention are either receiving devices in which an optical fiber brings the light up to a photodiode or phototransistor, or emitting devices in which a DEL or a semiconductive laser emits light towards an optical fiber.
In both cases, the most difficult problem to overcome is that of optimizing an optical head, since the luminous powers involved are very weak--1 to 20 milliwatts maximum except for a pulsed operation--and the dimensions of the objects to be positioned very small--50/125 micrometer for an optical fiber and 40 to 200 micrometers for an electro-optical semiconductor (it concerns the sensitive surface)--with a precision of more or less 1 to 10 microns. A misalignment of 3 micrometers in the alignment of an optical fiber on a laser produces an energy loss of 1 decibel.
Adjusting and aligning means operated up until now use either a mechanical pre-adjusting, the optical fiber being positioned in a groove provided in the support of the semiconductive device, or a dynamic adjusting, during which a drop of a photopolymerisable glue, supported by the optical fiber, is suddenly solidified by a flash of ultraviolet light at the moment when the optical fiber is well positioned.
The process according to the invention operates an optical head housing divided into at least two metallic parts--without counting the annex movable parts such as a closing cover or a joining connector, for example. On a first part of the housing is fixed the electro-optical solid state device, and if necessary the associated electronics; on the other part is fixed the optical fiber. One of the two parts comprises means for containing molten solder, such as an annular groove, or two or three cups. The other part comprises metallic means that plunge into the molten soldering bath. The length and the width of the molten soldering bath are sufficient to allow a free displacement of the first part of the housing with respect to the second part of the housing, along three orthogonal axes; this allows the adjusting of the optical fiber with respect to the semiconductor, during a dynamic positioning. When the optimal position of the fiber with respect to the semiconductor is reached, the soldering is cooled and solidified.